North Korea test-fired two medium-range ballistic missiles on Wednesday, South Korea and the US said, a defiant challenge to a rare three-way summit of its rivals Seoul, Tokyo and Washington that focused on the North’s security threat.

The launch of the Rodong missiles — for the first time since 2009 — violates UN Security Council resolutions and marks a big escalation from a series of shorter-range rocket launches the North has staged in recent weeks to protest ongoing annual military drills by the U.S. and South Korea that Pyongyang claims are invasion preparation.

The missiles flew about 650 kilometers off North Korea’s east coast early Wednesday morning, South Korean Defense Ministry spokesman Kim Min-seok said. It wasn’t immediately clear where the missiles splashed down. Kim said the missiles were likely fired from a mobile launcher.

The North’s arsenal of an estimated 300 Rodong missiles could in theory be fitted with nuclear warheads — once Pyongyang masters the ability to miniaturise atomic bombs — and, with a range of up to 1,300 kilometers, could reach Tokyo and key US military bases in Japan.

The US State Department later confirmed the launch of Rodong missiles and said North Korea apparently didn’t issue any maritime warning.

The launch comes on the fourth anniversary of the sinking of a South Korean warship that Seoul and other nations blame on a North Korean torpedo. Pyongyang denies involvement in the attack, which killed 46 sailors.

It also poses a big challenge to what had been recently improving relations between Pyongyang and Seoul. A year after threatening each other with war, the bitter rivals had restored some trust and held reunions of families divided by the Korean War of the early 1950s. The Korean Peninsula remains officially at war because that war ended with an armistice, not a peace treaty.